On 06/25/2013 12:11 PM, Leif Lindholm wrote: > This patch provides documentation of the [U]EFI runtime services and > configuration features. > diff --git a/Documentation/arm/uefi.txt b/Documentation/arm/uefi.txt > +The implementation depends on receiving pointers to the UEFI memory map > +and System Table in a Flattened Device Tree - so is only available with > +CONFIG_OF. > + > +It (early) parses the FDT for the following parameters: Part of this document (the raw requirements for DT content, rather than the discussion of OS implementation/behaviour in parsing/interpreting the properties) should be part of a file in Documentation/devicetree/bindings/ (arm/uefi.txt?). What node are these properties expected to be contained within? Shouldn't that node be required to contain a compatible value, which would define the schema for the other properties? > +- 'efi-system-table': > + Physical address of the system table. (required) > +- 'efi-runtime-mmap': > + Physical address of an EFI memory map, containing at least > + the regions to be preserved. (required) > +- 'efi-runtime-mmap-size': > + Size in bytes of the provided memory map. (required) > +- 'efi-mmap-desc-size': > + Size of each descriptor in the memory map. (override default) > +- 'efi-mmap-desc-ver': > + Memory descriptor format version. (override default) > + > +Since UEFI firmware on ARM systems are required to use a 1:1 memory map > +even on LPAE-capable systems, the above fields are 32-bit regardless. What about ARMv8? Is the intention to have a separate definition for the UEFI bindings on ARMv8, so that compatibility isn't an issue? What if a future version of UEFI allows LPAE usage? It may be better to explicitly state that the size of those properties is either #address-cells from the parent node (presumably the top-level of the DT), and/or introduce some property to explicitly state the size of the properties. Those mechanisms would allow forward-compatibility to LPAE usage or ARMv8 without requiring the text of the binding definition to change. Also, it seems legal to state the physical addresses using 64-bits even if the actual values themselves are restricted to 32-bit range by the UEFI spec. Illegal values would presumably cause SW that interprets them to fail error-checks, and be rejected. > +After the kernel has mapped the required regions into its address space, > +a SetVirtualAddressMap() call is made into UEFI in order to update > +relocations. This call must be performed with all the code in a 1:1 Presumably "all the code" also includes "all .data and .bss", or whatever the UEFI-equivalent may be? I'm not familiar with UEFI at all; does the "EFI memory map" mentioned above describe all the memory regions that must be mapped to use UEFI? > +mapping. This implementation achieves this by temporarily disabling the > +MMU for the duration of this call. This can only be done safely: > +- before secondary CPUs are brought online. > +- after early_initcalls have completed, sinze it uses setup_mm_for_reboot(). -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
